The issue is probably that we don't have accounts / are not logged into a system there like you are. :P
"The system is unable to access the cookie that was assigned to your computer upon login. The most likely cause of this problem is an improper access to the course via a bookmark, browser window that was left open, or an improper exit from the system.

Well, with the x-intercepts / our zeros of the graph, we can tell that x = 2 and x = -2 are solutions. That means in terms of a quadratic equation, we have k(x - a)(x - b) = 0: with 'a =2' and 'b = -2' (The extra k is because we could have an extra constant multiplied on there).
y = k(x - 2)(x + 2) = 0
y = k(x^2 - 4)
Then for the extra 'k', we just have to use (0, -4):
-4 = k(0^2 - 4)
-4 = k(-4)
1 = k
So, plug that in, we simply get: y = x^2 - 4
Looks a lot like a difference of two squares, right? :)